Process for making aluminum oxide from hydrated aluminum



Aug. 6, 1957 R. w. DINGMAN ETAL 2,301,901

PROCESS FOR MAKING ALUMINUM OXIDE FROM HYDRATED ALUMINUM SALZIS. FiledMarch 23. 1953 2 Sheets-Sheet l 0 M. Wm

INVEN TOR {MM Aft/42M Q. I

United States Patent Ofiice 2,801,901 Patented Aug. 6, 195 7 PROCESS FORMAKING ALUMINUM OXIDE FROM HYDRATED ALUMINUM Robert W. Dingman, Sharon,Laurent P. Michel, Watertown, Robert N. Secord, Reading, and William D.Schaelfer, Needham, Mass., assignors to Godfrey L.- Cabot, Inc., Boston,Mass., a corporation of Massachusetts Application March 23, 1953, SerialNo. 343,908

5 Claims. (Cl. 23-142) This invention relates to aluminum oxideproduction and comprises a novel process for producing aluminum oxidefrom salts of aluminum in the solid state.

Aluminum oxide is one of the more common industrial raw materials. It isavailable in varying degrees of purity and subdivision, in general thefiner and purer forms being the more valuable. The pigment grade is, byfar and away, the most important and most valuable grade of aluminumoxide, such being composed of particles averaging below about microns indiameter and having a purity of at least 95%.

Methods heretofore known for producing pigment grade aluminum oxides areof two general types: (1) an aluminum halide is oxidized or hydrolyzedin a flame and (2) an aluminum salt having combined oxygen is thermallydecomposed by external application of heat. Both of these types ofreaction, in the light of the present invention, have certaindisadvantages.

In carrying out a process of the first type the aluminum halide must beintroduced into the reaction zone as a vapor, which vapor is necessarilyat an elevated temperature. Conducting such but vapors through conduits,valves and instruments, while not impossible, is difiicult andcomplicates the process.

In carrying out a process of the second type heat to decompose the saltmust be conducted through the walls of a reactor or gas heater. Toprovide sufiicient heat in the reaction zone temperatures considerablygreater than those required for the reaction must be applied to theexternal walls and the walls must be relatively thin and be able towithstand high temperatures and conduct heat. Hence materials ofconstruction are of high cost and of short service life.

It is the principal object of this invention to provide a process andapparatus for producing pigment grade aluminum oxide from any aluminumsalt available as a solid at atmospheric conditions by reacting thesolid material in contact with a flame.

It is a further object of this invention to provide a process employinga universal reaction zone for any solid aluminum salt.

A further object of this invention is to provide a process and apparatusby and in which oxidation, hydrolysis or thermal decomposition of solidaluminum salts may be carried out in a turbulent flame supplied by acombustible gas and an oxygen-containing gas in such proportions thatthe nature, particle size and surface area of the resulting aluminumoxide product can be adjusted as desired.

In one aspect our invention comprises a process in which a solidaluminum salt, preferably powdered to facilitate handling, is introducedin a carrier gas into one end of an elongated heat insulated chamber andintermingled with a turbulent flame produced by burning a combustiblegas with an oxygen-containing gas, generally air, introduced into thesame end of the chamber. The.

various reactants are supplied to the reaction zone in 2 such mannerthat a cyclonic flame of high turbulence is provided and maximum mixingof aluminum raw material and combustibles and combustion products isachieved. Various means for providing such turbulent mixing may beemployed within the scope of our invention, the most convenient meansbeing to introduce one or more of the reactants tangentially into thechamber.

The reaction of the aluminum salt in the flame is rapid and theresulting aluminum oxide pigment is finely divided, the average particlesize being in the range 0.005 to 10 microns and the pigment having asurface area in the range 5 to square meters per gram, particle sizedecreasing and surface area increasing with increasing turbulence andgaseous dilution in the reaction zone. A particularly troublesomeproblem encountered in reactions involving the production of metaloxides from their salts is in the separation of reaction by-productsfrom the product oxide. In addition, when the salts are fusible, thereis a tendency for the particles to agglomerate with the result that theproduct may be both coarse and impure. The present invention avoidsthese difiiculties. By utilizing a cyclonic turbulent reaction zone,pigment size particles of aluminum oxide of high purity may readily beproduced.

While any aluminum salt which is solid at atmospheric conditions can beused in the process of our invention the following salts are preferred:basic aluminum acetate, aluminum benzoate, aluminum bromate, aluminumbromide, aluminum chlorate, aluminum chloride, aluminum iodide, aluminumnitrate, aluminum oleate, aluminum oxalate, aluminum salicylate,aluminum stearate, aluminum sulfate, and aluminum sulfide.

Going into more detail, we refer to the accompanying drawings inconnection with the following description of a preferred manner ofcarrying out the process of our invention, in which:

Fig. l is a flow sheet of the process,

Fig. 2 is a view in vertical cross section of one suitable type ofreactor, and

Fig. 3 is a View in vertical cross section of another suitable type ofreactor additionally showing one satisfactory means for delivering thesolid raw material to the reactor.

In carrying out the process according to the flow diagram of Fig. 1, thealuminum salt, which may have a small amount of oxide admixed therewithto prevent caking, is introduced through feed pipe 10 into an elongatedheat insulated reaction chamber 12. A mixture of gas and air inproportion such that there is suflicient air for theoretically completecombustion of the gas is introduced into the reactor through pipe 14.The inlet ends of pipes 10 and 14 are so positioned within the reactorwith respect to one another that the aluminum salt will be intimatelymixed with the combustion gases and hence with the resulting flame whenthe gases are ignited.

The bulk of the reaction by which the aluminum salt is converted toaluminum oxide and product: gases is completed Within reactor 12. Thereaction products are then conducted through flue 16 to separator 18which maybe of the cyclone, filter, or any other convenient type. In theseparator the solid oxide product is removed from the gases andrecovered through outlet pipe 20.

The gases now largely freed of their solid content are exhausted fromseparator 18 through conduit 22 and are either discharged into theatmosphere or preferably are passed into a scrubber 24 of conventionaldesign. As here illustrated spray liquid, consisting principally ofWater and Whatever neutralizing chemical may be required for theparticular aluminum salt in process, is introduced into the scrubberthrough pipe 26. Scrubbing liquid is discharged from the scrubberthrough pipe 28 and a portion may be recycled through pipe 30. Cleanedgases are discharged to the atmosphere through fan 32 and stack 34.

.It is apparent that the process of our invention can 4 in the rangebelow microns, it is essential that the reactant flame be turbulent andthat the reactant raw material be introduced directly into or in closejuxtaposition to the flame. The optimum condition is dispersion of thereadily be carried out in reactors of various design. It 5 aluminum saltthrough the burning combustion gases is merely necessary, as we havesaid, to provide a turso that the particles of aluminum oxide as theyform bulent flame and to introduce the aluminum salt in finely will bediluted by combustion product gases. Furtherdivided form directly in theflame. Suitable types of more, this arrangement provides for very rapidreaction reactor are shown in Figs. 2 and 3. and quick removal of theoxide product from the re- Referring first to Fig. 2, the reactor 12consists of a 0 action zone which is believed to be an important factorchamber having refractory walls 40 held in place by in achieving a fineparticle size material. steel shell 42. The inlet end is enclosed by acircular An important advantage of this invention is that it air header44 having a supply duct 46 preferably leading makes readily available awide variety of operating conthereinto in a direction tangent to theinner wall. Cenditions by which particle size and surface area of thetered in the inlig end of ttiedretactor 112 is an alllil'llnliil 15prodtilict can bi; varied and controlled;1 Thus, byhchangsaltrfeed pipesurroun e y a arger gas pipe 4 mg e rate 0 input 0 reactants an varyinge prothe two pipes 48 and 50 being concentrically disposed. portion ofdiluent gases to raw material a considerable In the operation of thisreactor powdered aluminum salt variety of productscan be obtained. issuspended in a suitable gas and carried into the re- More specifically,it would appear that by increasing actor through pipe 48. A mixture ofcombustible gas the ratio of air to combustible gas and hence increasingand air is introduced through pipe 50 and supplemental the ratio ofdiluents to raw material, the particle size air is supplied through duct46 and header 44. Comof the product may be decreased, provided, ofcourse bustible gas alone can be supplied through pipe 50 but that thereis always present at least sufficient air for it is preiergbe toprtejmix with thg gas a portion of 1the thegrelticaly conzpletiecgmbustion of the combustible gals. air require or com ustion in or erto insure comp ete s as een s a e a ove it is necessary to convey t e'burning of the gas. In entering tangentially through aluminum salt intothe reactor in a stream of gas. Obduct 46, the supplemental air producesan intensely turviously, the more finely powdered the aluminum salt,bulent cyclonic flame within the reaction zone. the more easily canthis. raw material be delivered in Another design of suitable reactor isshown in Fig. 3. the gas. The carrier gas itself may be chosen with re-In this type of reactor powdered aluminum salt is inspect to the desiredproportions of reactant gases. When tfoglceg theregto ghro tgglpipe 56,vfill'tllll seClilhol'l 5g a iargg exeess of ldilgient a1r(i)srglquiregl, tllile ciarrifer gas an 'ee pipe suia e carrier gas passingroug W1 a van ageousy e an. n e ot er an i more the venturi section offeed pipe 64 inspirates the powdered om stible gas is required in closecontact with the aluminum salt and carries it into a short, largediameter raw material a combustible gas can be used. An inert combustionchamber 62. A mixture of gas and air is carrier gas is likewise withinthe contemplation of this introduced into a circular combustion chamber62 through invention. A pipe 64 in a direction tangent to the inner wallof the In the following examples are set forth data from h b so th t arapidly whirling fl e i developed various runs carried out in accordancewith our inventherein. Chamber 62 communicates with a long tubular t n.chamber 66 of smaller diameter in which reaction is 40 Example 1completed. By reason of the reduction in diameter within the reactionchamber 12, great cyclonic turbulence The i q runs were m In apparatusof the yp is developed inbcombustion chamber 62 and very rapid 1 x? 111l li edl the aluminum Salt raw material being mixing of com ustiongases, combustion products and "111m 0 on aluminum salt takes place. a

If additional heat or diluent gases are required they R N may besupplied downstream from the combustion chamo 192 195 198 205 195'2 herthrough conduit 68 also preferably directed tangent Aluminum chlorideper hr M 8J5 91 (L8 to the inner wall of the chamber. ACflmguitililiegas, 0. F. rn as 5.5 4.8 5.0 as

0 I s I l n 2 It will be apparent that various modifications in operat-Yield A1403, percent of theoretical V g 29 g? i3 52 mg methods may beemployed. For example, with the 120 1; lprofductipnillbs. per hour 3 1.13.1 .7 .s

t en 0 runm ur .66 2.7 2. reactor of Figure 2 aluminum salt can beintroduced suffice prsoduct 70.2 2 g through pipe 50 and the combustiblegas or mixture of Average particle size, mi]1i.microns 26.0 43.5 32.534.4 39.6 gas and air can be supplied through pipe 48. 55

Likewise in the operation of reactor of Fig. 3 the E l 2 aluminum saltcan be introduced into the combustion xamp 8 Chamber tangeHt 1a11ythrough Fondult 64 Whlle gas and The following runs were made inapparatus similar 81f can PP thlfollgh P 1 In all events, the to thatillustrated in Figure 3, the aluminum salt being iced conduits can besized as required for optimum perfi ly ground hydrated aluminum sulfateormance.

For satisfactory operation of the process of our in- (Al2(SO4)3.16.5HzO)vention, by which is meant the production of pigment grade aluminumoxide having an average particle size of which being finer than mesh.

Run No s 7 s 10 11 12 13 i 14 Combustible gas. City City City CityHydrogen. Hydrogen- Hydrogen- Hydrogen. Atmosphere Reducing-Reducingoxidizing. Reducing- Reducing. Reducing- Reducing.gegggttekagiaper 1.11 7.62 3.3 472 9.72 4.72 4.76 (25.70. centb t.Combusii ie gas, 0. F. H.-. 162. Air, 0. F.H 285. Flame temp., F 1,670.Ni surface area of pro 33.7.

We claim:

1. The method of producing finely divided aluminum oxide comprisingsuspending solid particles of a hydrated aluminum salt in a carrier gas,introducing the suspension axially into a heat insulated elongatedcircularly cylindrical reaction chamber and simultaneously introducinginto said reaction chamber a combustible gas and a freeoxygen-containing gas, at least one of said gases being introducedtangentially against the wall of said chamber to create a cyclonicturbulent reaction Zone, the oxygen containing gas being in an amount atleast sufficient to burn the combustible gas and to convert the aluminumsalt to the oxide, burning said combustible gas to maintain atemperature within the reaction chamber sufficient to convert thealuminum salt to aluminum oxide, and recovering the aluminum oxide fromthe gaseous reaction products.

2. The method defined by claim 1 in which the aluminum salt is carriedinto the reaction zone by air as the carrier gas.

3. The method defined by claim 1 in which the aluminum salt is carriedinto the reaction zone by a combustible carrier gas.

4. The method defined by claim 1 in which the aluminum salt isintroduced into the reaction zone suspended in a stream of combustiblegas and air is introduced tangentially thereabout as a whirling annularstream surrounding the combustible gas.

5. The method defined by claim 1 in which the aluminum salt is selectedfrom the group consisting of aluminum chloride and aluminum sulfate.

References Cited in the file of this patent UNITED STATES PATENTS1,816,388 Mittasch July 28, 1931 1,850,286 Mittasch Mar. 22, 19322,155,119 Ebner Apr. 18, 1939 2,659,662 Heller Nov. 17, 1953 FOREIGNPATENTS 258,313 Great Britain Sept. 15, 1926 661,685 Great Britain Nov.28, 1951 OTHER REFERENCES Serial No. 379,872, Ebner (A. P. 0.),published April 27, 1943.

1. THE METHOD OF PRODUCING FINELY DIVIDED ALUMINUM OXIDE COMPRISINGSUSPENDING SOLID PARTICLES OF A HYDRATED ALUMINUM SALT IN A CARRIER GAS,INTRODUCING THE SUSPENSION AXIALLY INTO A HEAT INSULATED ELONGATEDCIRCULARLY CYLINDRICAL REACTION CHAMBER AND SIMULTANEOUSLY INTRODUCINGINTO SAID REACTION CHAMBER A COMBUSTIBLE GAS AND A FREEOXYGEN-CONTAINING GAS, AT LEAST ONE OF SAID GASES BEING INTRODUCEDTANGENTIALLY AGAINST THE WALL OF SAID CHAMBER TO CREATE A CYCLONICTURBULENT REACTION ZONE, THE OXYGEN-CONTAINING GAS BEING IN AN AMOUNT ATLEAST SUFFICIENT TO BURN THE COMBUSTIBLE GAS AND TO CONVERT THE ALUMINUMSALT TO THE OXIDE, BURING SAID COMBUSTIBLE GAS TO MAINTAIN A TEMPERATUREWHITHIN THE REACTION CHAMBER SUFFICIENT TO CONVERT THE ALUMUNUM SALT TOALUMINUM OXIDE, AND RECOVERING THE ALUMINUM OXIDE FROM THE GASEOUSREACTION PRODUCTS.